Design and Synthesis of Nitro Cage Heterocycles as Energetic Materials Derived from Pentacycloundecane (PCUD) Systems

Abstract

AbstractA variety of pentacycloundecane (PCUD) based cage compounds containing nitro groups were synthesized via a simple synthetic method starting with cage diones. Eight PCUDs were used for nitro functionalization. These cage diones were prepared starting with easily accessible starting materials such as 2,3‐dimethylhydroquinone, 1,4‐dihydroxybenzene, and cyclopentadiene. Here, we have used Diels‐Alder (DA) reaction, [2+2] photocycloaddition, and Henry reaction as key steps. Transannular cyclization plays an important role to generate a nitro substituted cage heterocycles via base promoted reaction using nitromethane as a reagent. Some of these oxa‐cage structures have been further supported by single‐crystal X‐ray diffraction studies. Energetic performance of the title compounds was evaluated using DFT based calculations. These bis(nitromethyl)octahydro‐1H‐1,3,4,6(epiethane‐[1,1,2,2]tetrayl)‐pentaleno[1,6‐bc]furan analogues (11 b–18 b) owned the densities in the range of 1.37–1.60 g/cm3. All the studied compounds possess high positive enthalpy of formation (33.68–230.48 kJ/mol, except compound with dimethyl groups (16 b, −11.38 kJ/mol) and very good thermal (Tm=99–147 °C) and kinetic stabilities. Ammonium perchlorate based various propulsion formulations suggests that these compounds could be excellent candidates in the solid rocket propulsion.